Hard disk drives are mass storage devices that include a magnetic storage media, e.g. rotating disks or platters, a spindle motor, read/write heads, an actuator, a pre-amplifier, a read channel, a write channel, a servo circuit, and control circuitry to control the operation of hard disk drive and to properly interface the hard disk drive to a host system or bus. FIG. 1 shows an example of a prior art disk drive mass storage system 10. Disk drive system 10 interfaces with and exchanges data with a host 32 during read and write operations. Disk drive system 10 includes a number of rotating platters 12 mounted on a base 14. The platters 12 are used to store data that is represented as magnetic transitions on the magnetic platters, with each platter 12 coupleable to a head 16 which transfers data to and from a preamplifier 26. The preamp 26 is coupled to a synchronously sampled data (SSD) channel 28 comprising a read channel and a write channel, and a control circuit 30. SSD channel 28 and control circuit 30 are used to process data being read from and written to platters 12, and to control the various operations of disk drive mass storage system 10. Host 32 exchanges digital data with control circuit 30.
Data is stored and retrieved from each side of the magnetic platters 12 by heads 16 which comprise a read head 18 and a write head 20 at the tip thereof. The conventional readhead 18 and writehead 20 comprise magneto-resistive heads adapted to read or write data from/to platters 12 when current is passed through them. Heads 16 are coupled to preamplifier 26 that serves as an interface between read/write heads 18/20 of disk/head assembly 10 and SSD channel 28. The preamp 26 provides amplification to the waveform data signals as needed. A preamp 26 may comprise a single chip containing a reader amplifier 27, a writer amplifier, fault detection circuitry, and a serial port, for example. Alternatively, the preamp 26 may comprise separate components rather than residing on a single chip.
To achieve high write speeds it is desired to provide a large voltage swing and a fast slew-rate current to the write head 120. A typical way to deliver a large voltage swing and fast slew-rate current via an interconnection to a thin film head is to use large CMOS levels and capacitors to boost the write driver's current and voltage. However, the disadvantages are that a large CMOS voltage swing (5V) causes too much power supply glitching, resulting in serious data pattern dependency and jitter. Currently, the most advanced write driver using CMOS-level switches can not operate over about 1.2 Gb/s.
Moreover, due to the flex cable interconnection between the preamplifier's write driver circuit and the thin film head, the current and voltage delivered to the thin film head are limited. Thus, a new write driver circuit is needed to overcome this problem so that data can be written at a higher data rates (1.2 Gb/s to 1.8 Gb/s).